1. Field of the Invention
The invention relates to an evaporated fuel treatment device and an evaporated fuel treatment method for treating an evaporated fuel generated within a fuel tank (for example, a fuel tank for a vehicle) without discharging the evaporated fuel to the atmosphere. More specifically, the invention relates to elimination of the failure resulting from direct introduction of the evaporated fuel within the fuel tank into an intake system of an internal combustion engine.
2. Description of the Related Art
A canister system (evaporated fuel treatment device) for preventing discharge of the evaporated fuel generated within the fuel tank into the atmosphere is well known as being provided for the fuel supply system in an engine for a vehicle. For example, such publications as JP-A-2004-156495 and JP-A-2004-156492 disclose the canister system in which the evaporated fuel generated within the fuel tank is temporarily adsorbed in a charcoal canister (hereinafter simply referred to as a canister) such that the evaporated fuel within the canister is introduced (purged) into an intake pipe of the engine under the negative pressure of the intake air in the intake system of the engine upon establishment of a predetermined purge condition.
The canister system disclosed in the above described publications is provided with a vapor pipe that connects the fuel tank with the canister, a purge pipe that connects the canister with the intake pipe of the engine, and an atmospheric introduction pipe that communicates the atmosphere with the inside of the canister.
The vapor pipe is provided with a closing valve unit that is capable of cutting the communication between the fuel tank and the canister. The closing valve unit includes a closing valve as an electromagnetic valve which is capable of switching between an opened state and a closed state, and a relief valve connected in parallel with the closing valve. The purge pipe includes a purge control valve (hereinafter referred to as a purge VSV) as an electrically operated valve or a motor valve for controlling a flow rate of the evaporated fuel flowing to the intake pipe. The atmospheric introduction pipe includes an OBD (On-Board Diagnostic System) pump module for controlling introduction of the atmospheric pressure into the canister. The OBD pump module includes a switching valve that switches the communication state of the atmospheric pressure with the canister between a communication state and a non-communication state, and a motor pump for applying the negative pressure into the canister system during the failure diagnosis.
JP-A-2004-156495 discloses that the purge VSV is forcibly closed upon supply of the fuel into the fuel tank during the engine operation. This makes it possible to prevent direct purging of the evaporated fuel into the engine intake system from the purge pipe so as not to bring the engine into the unstable operation state even if the closing valve is opened so as to prevent discharge of the evaporated fuel generated within the fuel tank into the atmosphere from the feed pipe.
In the above-described canister system, when a failure, for example, hole, crack, or poor sealing occurs in the fuel tank, the canister, or the like, the evaporated fuel may leak out of the portion at which such failure occurs. In the case where error occurs in the assembly of the pipe during the process of manufacturing the vehicle, the evaporated fuel may also leak to the outside. It is therefore important for the canister system of the aforementioned type to immediately locate the portion that causes the leakage of the evaporated fuel. For this, the engine is operated to apply the negative pressure of the intake air in the intake system to the canister system such that it is diagnosed whether there exists a position that causes the leakage of the evaporated fuel based on the introduced negative pressure. As the negative pressure of intake air tends to take a relatively high value, the above-described diagnosis may be performed for a shorter period.
Generally a failure diagnosis tool is connected to a controller (ECU) for controlling the aforementioned valves and the motor pumps such that a failure diagnosis signal is sent from the failure diagnosis tool to the controller. Upon receipt of such signal, the controller performs the failure diagnosis (determines whether there is a failure point that causes the leakage of the evaporated fuel, diagnoses operations of the valves and motor pumps) while operating those valves and pumps in accordance with the predetermined procedure.
In the case where the position of the switching valve of the OBD pump module is forcibly switched from OFF to ON upon diagnosis of the operation of the OBD pump module, the introduction of the atmospheric pressure into the canister is cut. Meanwhile during the engine operation, the purge control is normally executed. Accordingly when a predetermined purge condition is established, the purge VSV is expected to be opened. When the purge condition is established in a state where the introduction of the atmospheric pressure into the canister is cut by forcibly switching the position of the switching valve of the OBD pump module from OFF to ON as described above, the negative pressure of intake air in the intake system is introduced into the canister as the purge VSV is opened. The pressure within the canister becomes considerably lower than the pressure within the fuel tank. The resultant differential pressure serves to open the relief valve of the closing valve unit, and as a result, the evaporated fuel within the fuel tank is directly purged into the intake system of the engine. In the aforementioned state, the density of the fuel in the mixture becomes excessively high to bring the engine into the unstable operation state, and as the case may be, the engine operation is stopped.
The aforementioned failure may occur not only in the case of forcibly switching the position of the switching valve for diagnosing the operation of the OBD pump module but also in the case of switching the position of the switching valve caused by the operation error.
Further the aforementioned failure may occur not only in the case of switching the position of the switching valve of the OBD pump module but also in the case of forcibly or erroneously driving the motor pump of the OBD pump module, and forcibly or erroneously opening the closing valve.